A voltage-gated nanochannel-based isobaric ion screening system and method

Abstract

The application discloses a same-valence ion screening system and method based on a voltage-gated nanochannel, which comprises a power supply, Ag / AgCl electrodes, an electrolyte solution, a pure water solution and a nanochannel device comprising a silicon substrate, a silicon nitride layer, a metal electrode layer and a nanochannel; the silicon nitride layer and the metal electrode layer are periodically and alternately stacked into a film, the silicon substrate is installed at the bottom of the film, and the nanochannel penetrates through the silicon substrate and the film; the power supply comprises a driving voltage power supply and two gate voltage power supplies, the driving voltage power supply is connected with the two Ag / AgCl electrodes respectively, and the electrodes are respectively inserted into the electrolyte solution and the pure water solution; and the two gate voltage power supplies are periodically and alternately connected with the metal electrode layer. The method realizes the screening of ions through multistage low-potential area capture and release, has good selectivity, high separation efficiency, safety and non-toxicity, can realize large-scale precise control separation, and solves the problem that the prior art cannot separate same-valence charge ions with close sizes.

Description

Technical Field

[0001] This invention belongs to the field of artificial nanochannels, and in particular relates to a isovalent ion screening system and method based on voltage-gated nanochannels. Background Technology

[0002] Biological ion channels are located within cell membranes. They utilize size effects or electrostatic effects of functional groups on the channel walls to allow only ions of a certain size or charge to pass through, such as potassium ion channels (KcsA) and sodium ion channels (NavAb), which are selective for specific types of ions (potassium or sodium). Ion channels are key components in many biological processes, playing a role in transmitting nerve signals and regulating muscle movement through the selective transport of specific ions. When the ion selectivity of a channel decreases, it can lead to disorders in overall physiological function and the development of certain diseases. The unstable structure and performance of natural ion channels have prompted researchers to create various artificial nanochannels for screening different ions. These are mainly solid-state nanochannels, including carbon nanotubes, graphene nanochannels, and silicon nitride nanochannels. Compared with natural biological ion channels, artificial nanochannels have advantages such as better mechanical stability, tunable geometry and surface properties, and ease of integration. These artificial channels play important roles in fields such as biomolecular detection, salinity gradient power generation, energy storage, and ion detection.

[0003] Currently, artificial nanochannels primarily utilize size and electrostatic effects to separate different ions. Regarding the size effect of nanochannels, ion selectivity mainly stems from differences in ion size and hydration energy. This method easily separates ions with large size differences, often requiring nanochannel diameters strictly less than 1 nanometer. However, large-scale and precise fabrication of nanochannels of this size remains extremely difficult. Existing micro / nano fabrication technologies, such as focused ion beam (FIB) technology, can only controllably fabricate nanochannels with a minimum diameter of approximately 5 nanometers, and transmission electron microscopy (TEM) can only fabricate nanochannels with a minimum diameter of approximately 2 nanometers, resulting in poor ion selectivity. Regarding the electrostatic effect of nanochannels, functional groups are modified on the nanochannel surface, and ions are screened based on the binding characteristics of these functional groups to corresponding ions. This method is suitable for ions with large charge differences or ions with different polarities. Both of these methods remain challenging for separating ions with similar sizes and the same valence charge, such as alkali metal ions like lithium, sodium, and potassium, or halide ions like chlorine, bromine, and iodine. Furthermore, since the selectivity of nanochannels is determined by the channel's geometry and chemical properties, each target ion must be individually designed.

[0004] Other researchers have screened ions by utilizing the binding properties of crown ethers to corresponding ions. The pores within the crown ether ring and alkali metal ions are matched according to their diameters; for example, 12-crown ether-4 selectively binds lithium ions, 15-crown ether-5 binds sodium ions, and 18-crown ether-6 binds potassium ions. However, the crown ether modification process on the surface of nanochannels cannot be precisely controlled and is unstable. Furthermore, crown ethers are required in large quantities and possess a certain degree of toxicity, making them unsuitable as replacements for biological ion channels. Summary of the Invention

[0005] To address the aforementioned technical shortcomings, the present invention aims to provide a voltage-gated nanochannel-based isovalent ion screening system and method. This system controls the surface potential of the nanochannel walls by adjusting the voltage of the gated voltage source. Utilizing the proportionality between ion velocity and diffusion coefficient, ions are allowed to move through the nanochannel at different speeds. After being captured and released through multiple low-potential regions, ion screening is ultimately achieved. This method offers high selectivity, high separation efficiency, safety, and non-toxicity, enabling large-scale, precise control and separation. It solves the problem that existing technologies cannot separate isovalent ions of similar size.

[0006] The first objective of this invention is to provide a voltage-gated nanochannel-based isovalent ion screening system, comprising a power supply, an Ag / AgCl electrode, an electrolyte solution, a pure aqueous solution, and a nanochannel device;

[0007] The nanochannel device includes a silicon substrate, a silicon nitride layer, a metal electrode layer, and a nanochannel; the silicon nitride layer and the metal electrode layer are periodically stacked alternately to form a thin film, the silicon substrate is installed at the bottom of the thin film, and the nanochannel penetrates through the silicon substrate and the thin film;

[0008] The power source includes a driving voltage power source, a gated voltage source one, and a gated voltage source two; the electrolyte solution contains isovalent ions to be screened; the driving voltage power source is connected to two Ag / AgCl electrodes, which are respectively inserted into the electrolyte solution and the pure aqueous solution; the gated voltage source one and the gated voltage source two are periodically and alternately connected to the metal electrode layer.

[0009] Furthermore, the diameter of the nanochannel is 5-20nm, comprising n+1 silicon nitride layers with a thickness of 20-30nm, 2n metal electrode layers with a thickness of 5-10nm, and n silicon nitride layers with a thickness of 10-15nm stacked periodically, wherein n ranges from 3 to 6, which can achieve ion separation while avoiding increased resistance and reduced ion flow.

[0010] Furthermore, the metal electrode layer is a conductive and easily deposited material, including a gold electrode layer, a platinum electrode layer, or an aluminum electrode layer.

[0011] Furthermore, the driving voltage power supply is a DC voltage source, which applies a constant voltage along the nanochannel axis through the Ag / AgCl electrode to drive the ions to move directionally along the nanochannel axis.

[0012] Furthermore, the first gated voltage source and the second gated voltage source are variable voltage sources, which apply periodic voltages to the nanochannel walls through the metal electrode layer to control the surface potential of the nanochannel walls.

[0013] The second objective of this invention is to provide a method for fabricating a nanochannel device, the specific steps of which are as follows:

[0014] A1: A silicon nitride layer was deposited on a silicon substrate using dichlorosilane and ammonia via low-pressure chemical vapor deposition, and the thickness of the silicon nitride layer was observed by elliptic polarization spectroscopy.

[0015] A2: A metal electrode layer was deposited on the silicon nitride layer by magnetron sputtering, and the thickness of the metal electrode layer was observed by a quartz crystal microbalance.

[0016] A3: Then, a silicon nitride layer is deposited, followed by a metal electrode layer. This process is repeated to obtain a thin film in which the silicon nitride layer and the metal electrode layer are periodically stacked. The thickness of the silicon nitride layer and the metal electrode layer is controlled by changing the deposition time, temperature, pressure, etc.

[0017] A4: By combining photolithography and reactive ion etching, a release window is created on the bottom silicon substrate using a potassium hydroxide solution;

[0018] A5: By using focused ion beam technology to penetrate the thin film, a nanochannel is formed that runs through the silicon nitride layer and the metal electrode layer. The diameter of the nanochannel is adjusted by controlling the intensity and time of the ion beam.

[0019] A6: Wires are led out from the edge of the metal electrode layer by electron beam induced deposition to facilitate connection to a gated voltage source;

[0020] A7: Finally, connect the nanochannel device to the driving voltage power supply, gate voltage source one and gate voltage source two, and Ag / AgCl electrode, and place it between the electrolyte solution and the pure water solution to ensure that the solution in the two liquid pools can only flow through the nanochannel.

[0021] The third objective of this invention is to provide a method for isovalent ion screening based on a voltage-gated nanochannel isovalent ion screening system, comprising the following steps:

[0022] B1: A constant voltage is applied by a driving voltage power supply, so that isovalent ions are captured and enter the nanochannel and move along the axis of the nanochannel. The Ag / AgCl electrode on the electrolyte solution side is grounded, and the voltage on the pure aqueous solution side is negative.

[0023] B2: By adjusting the voltages of gated voltage source one and gated voltage source two, the surface potential of the nanochannel is adjusted, allowing ions to move through the nanochannel at different speeds with different ion diffusion coefficients. By applying a negative square wave pulse voltage to gated voltage source one and a positive square wave pulse voltage to gated voltage source two with the same pulse frequency, the ions are captured and released through multiple low-potential regions. The distance of the ions along the axial direction of the nanochannel gradually increases and they are completely separated, ultimately achieving ion screening.

[0024] B3: The screening process for isovalent anions is similar to that for isovalent cations. The difference is that when screening anions, the pure aqueous solution side is under a positive voltage. The anions are captured and released by the high potential region, thus achieving separation.

[0025] Furthermore, the specific process of step B2 is as follows:

[0026] S1: When the first gate voltage source is negative and the second gate voltage source is positive, a Brownian ratchet-like surface potential is formed on the nanochannel wall. Isovalent ions are captured at the wall at the first low potential and stop moving.

[0027] S2: When the voltages of gate voltage source one and gate voltage source two become 0, the ions are released by the wall and move slowly along the nanochannel axis under the constant voltage of the driving voltage power supply. The movement speed of the ions is proportional to the ion diffusion coefficient, that is, the ions with a larger diffusion coefficient move faster.

[0028] S3: When the first gate voltage source is negative and the second gate voltage source is positive, a Brownian ratchet-like surface potential is formed on the nanochannel wall again. At this time, the slow-moving ions do not enter the second low potential region, while the fast-moving ions are close to the second low potential region. Therefore, the fast-moving ions are captured at the wall at the second low potential, while the slow-moving ions are still captured at the wall at the first low potential. The distance of different ions along the nanochannel axis changes.

[0029] S4: The above process is repeated, and after being captured and released in multiple low potential regions, the distance between different ions along the axis of the nanochannel gradually increases and they are completely separated. Fast-moving ions move through the nanochannel, while slow-moving ions remain in the nanochannel or are captured in the first low potential region, thus achieving ion screening.

[0030] Furthermore, for ions with different diffusion coefficients, such as those with particularly small or large differences, different silicon nitride layer thicknesses can be achieved by controlling the process during nanochannel fabrication. The positional differences caused by the different diffusion coefficients of different ions can be further enhanced by adjusting the number of metal electrode layers. Alternatively, ion screening can be achieved by adjusting the square wave pulse size and frequency of gate voltage source one and gate voltage source two, as well as the voltage of the driving voltage power supply.

[0031] The beneficial effects of this invention are as follows:

[0032] 1. This invention controls the surface potential of the nanochannel by adjusting the voltage of the gated voltage source and applying a periodic voltage to the metal electrode layer. The ion velocity is proportional to the ion diffusion coefficient, allowing ions to move through the nanochannel at different speeds. After being captured and released in multiple low-potential regions, the ions gradually increase their distance along the nanochannel axis and are completely separated, ultimately achieving ion screening. This method has good selectivity, high separation efficiency, and is safe and non-toxic, solving the problem that existing technologies cannot separate ions with similar valence charges of similar size.

[0033] 2. The method of this invention can perform large-scale, precise control separation, is highly adaptable, and can adapt to the separation of various ions. It has the potential to be applied in fields such as biomolecular detection, salinity gradient power generation, energy storage, and ion detection. For ions with different diffusion coefficients, such as those with particularly small or large differences, different silicon nitride layer thicknesses can be achieved by controlling the process during the fabrication of nanochannels. The positional differences caused by the different diffusion coefficients of different ions can be further enhanced by adjusting the number of metal electrode layers. Alternatively, ion screening can be achieved by adjusting the square wave pulse size and frequency of gate voltage source one and gate voltage source two, as well as the voltage of the driving voltage power supply. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a voltage-gated nanochannel-based isovalent ion screening system according to Embodiment 1 of the present invention;

[0036] Figure 2 This is a schematic diagram illustrating the ion screening method and principle of Embodiment 1 of the present invention;

[0037] In the figure, 1. Driving voltage power supply; 2. Gated voltage source one; 3. Ag / AgCl electrode; 4. Ion A; 5. Ion B; 6. Electrolyte solution; 7. Gated voltage source two; 8. Metal electrode layer; 9. Silicon nitride layer; 10. Silicon substrate; 11. Nanochannel; 12. Pure aqueous solution. Detailed Implementation

[0038] The inventive method of this invention will be described and illustrated in detail below with specific examples. This description is intended to explain the invention and not to limit its scope of protection.

[0039] Example 1: Isovalent Ion Screening System

[0040] like Figure 1 As shown, the isovalent ion screening system based on voltage-gated nanochannels of the present invention includes a power supply, an Ag / AgCl electrode 3, an electrolyte solution 6, a pure aqueous solution 12, and a nanochannel device; the power supply includes a driving voltage power supply 1, a first gate voltage source 2, and a second gate voltage source 7; the electrolyte solution contains isovalent ions A4 and B5 to be screened; the nanochannel device includes a silicon substrate 10, a silicon nitride layer 9, a metal electrode layer 8, and a nanochannel 11; the driving voltage power supply 1 is connected to two Ag / AgCl electrodes 3, which are respectively inserted into the electrolyte solution 6 and the pure aqueous solution 12; the first gate voltage source 2 and the second gate voltage source 7 are periodically alternately connected to the metal electrode layer 8.

[0041] The nanochannel 11 has a diameter of 5-20 nm and a length of about 200 nm, and includes 5 silicon nitride layers 9 with a thickness of 20-30 nm, 8 metal electrode layers 8 with a thickness of 5-10 nm, and 4 silicon nitride layers 9 with a thickness of 10-15 nm, which are periodically stacked alternately.

[0042] The metal electrode layer 8 of the nanochannel device includes conductive and easily deposited materials such as gold electrode layer, platinum electrode layer or aluminum electrode layer. Preferably, the metal electrode layer 8 used in this embodiment is a gold electrode layer.

[0043] The driving voltage power supply 1 is a DC voltage source. A constant voltage is applied along the axial direction of the nanochannel through the Ag / AgCl electrode 3, driving ions to move directionally along the axial direction of the nanochannel 11.

[0044] The gated voltage source 12 and gated voltage source 27 are variable voltage sources. They apply periodic voltages to the walls of the nanochannel 11 through the metal electrode layer 8 to control the surface potential of the nanochannel 11 walls.

[0045] Example 2: Fabrication process of the nanochannel device

[0046] The fabrication process of the nanochannel device in Embodiment 1 is as follows:

[0047] A1. A silicon nitride layer 9 was deposited on a silicon substrate 10 using dichlorosilane and ammonia by low-pressure chemical vapor deposition, and the thickness of the silicon nitride layer 9 was observed by elliptic polarization spectroscopy.

[0048] A2. A metal electrode layer 8 is deposited on the silicon nitride layer 9 by magnetron sputtering, and the thickness of the metal electrode layer 8 is observed by a quartz crystal microbalance.

[0049] A3. Then, a silicon nitride layer 9 is deposited, followed by a metal electrode layer 8. This process is repeated to obtain a thin film in which the silicon nitride layer 9 and the metal electrode layer 8 are periodically stacked. The thickness of the silicon nitride layer 9 and the metal electrode layer 8 is controlled by changing the deposition time, temperature, pressure, etc.

[0050] A4. By combining photolithography and reactive ion etching, a release window is created on the bottom silicon substrate 10 using potassium hydroxide solution.

[0051] A5. By using focused ion beam technology to penetrate the thin film, a nanochannel 11 is formed that runs through the silicon nitride layer 9 and the metal electrode layer 8. The diameter of the nanochannel 11 is adjusted by controlling the intensity and time of the ion beam.

[0052] A6. Lead wires are drawn out from the edge of the metal electrode layer 8 by electron beam induced deposition to facilitate connection to the gated voltage source.

[0053] A7. Finally, connect the nanochannel device to the driving voltage power supply 1, gate voltage source 1 2 and gate voltage source 2 7, and Ag / AgCl electrode 3, and place it between the electrolyte solution 6 and the pure water solution 12 to ensure that the solution in the two liquid pools can only flow through the nanochannel 11.

[0054] Example 3 Ion Screening Method

[0055] like Figure 2 As shown, taking the screening of isovalent cations as an example, the specific ion screening method of the isovalent ion screening system based on voltage-gated nanochannels is as follows:

[0056] B1. A constant voltage is applied by the driving voltage power supply 1, so that ions A and B are captured and enter the nanochannel 11 and move along the axial direction of the nanochannel 11. The Ag / AgCl electrode 3 on the electrolyte solution 6 side is grounded, and the voltage on the pure aqueous solution 12 side is negative.

[0057] B2. By adjusting the voltages of gated voltage source 12 and gated voltage source 27, the surface potential of the nanochannel 11 is adjusted, causing ions A and B to move through the nanochannel 11 at different speeds, where the diffusion coefficient of ion A is greater than that of ion B. A negative square wave pulse voltage is applied by gated voltage source 12 and a positive square wave pulse voltage is applied by gated voltage source 27, with the same pulse frequency. The specific process is as follows:

[0058] Step 1. When gate voltage source 1 is negative and gate voltage source 2 is positive, a Brownian ratchet-like surface potential is formed on the wall of nanochannel 11. Ions A and B are captured at the wall at the first low potential and stop moving.

[0059] Step 2. When the voltage of gate voltage source 1 2 and gate voltage source 2 7 becomes 0, ions A and B are released by the wall and move slowly along the axis of nanochannel 11 under the constant voltage of driving voltage power supply 1. The movement speed of ions A and B is proportional to the ion diffusion coefficient, that is, ion A moves faster than ion B.

[0060] Step 3. When gate voltage source 1 is negative and gate voltage source 2 is positive, a Brownian ratchet-like surface potential is formed on the wall of nanochannel 11 again. At this time, ion B moves slowly and does not enter the second low potential region, while ion A moves quickly and is close to the second low potential region. Therefore, ion A is captured at the wall at the second low potential, while ion B is still captured at the wall at the first low potential. The distance between ion A and ion B along the axial direction of nanochannel 11 changes.

[0061] Step 4. The above process is repeated. After four levels of low potential regions for capture and release, the distance between ion A and ion B along the axial direction of nanochannel 11 gradually increases and they are completely separated. Ion A moves through nanochannel 11, while ion B remains in nanochannel 11 or is captured in the first low potential region, thus achieving the screening of ion A and ion B.

[0062] B3. The screening process for isovalent anions is similar to that for isovalent cations. The difference is that when screening anions, the pure aqueous solution is subjected to a positive voltage on side 12. The anions are captured and released by the high potential region, thus achieving separation.

[0063] B4. For ions with different diffusion coefficients, such as those with particularly small or large differences, ion screening can be achieved by controlling the process during the fabrication of nanochannel 11 to achieve different thicknesses of silicon nitride layer 9; ion screening can also be achieved by adjusting the number of metal electrode layers 8 to further enhance the positional differences caused by the different diffusion coefficients of different ions; ion screening can also be achieved by adjusting the square wave pulse size and frequency of gate voltage source 1 2 and gate voltage source 2 7, as well as the voltage of driving voltage power supply 1.

[0064] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A voltage-gated nanochannel-based isovalent ion screening system, characterized in that, Includes power supply, Ag / AgCl electrode, electrolyte solution, pure aqueous solution, and nanochannel device; The nanochannel device includes a silicon substrate, a silicon nitride layer, a metal electrode layer, and a nanochannel; the silicon nitride layer and the metal electrode layer are periodically stacked alternately to form a thin film, the silicon substrate is installed at the bottom of the thin film, and the nanochannel penetrates through the silicon substrate and the thin film; The power supply includes a driving voltage power supply, a gated voltage source one, and a gated voltage source two; the electrolyte solution contains isovalent ions to be screened; the driving voltage power supply is connected to two Ag / AgCl electrodes, which are respectively inserted into the electrolyte solution and the pure aqueous solution; The gated voltage source one and the gated voltage source two are periodically and alternately connected to the metal electrode layer, respectively.

2. The isovalent ion screening system based on voltage-gated nanochannels according to claim 1, characterized in that: The nanochannel has a diameter of 5-20 nm and consists of n+1 silicon nitride layers with a thickness of 20-30 nm, 2n metal electrode layers with a thickness of 5-10 nm, and n silicon nitride layers with a thickness of 10-15 nm stacked periodically, where 3≤n≤6.

3. The isovalent ion screening system based on voltage-gated nanochannels according to claim 1, characterized in that: The metal electrode layer is a conductive and easily deposited material, including a gold electrode layer, a platinum electrode layer, or an aluminum electrode layer.

4. The isovalent ion screening system based on voltage-gated nanochannels according to claim 1, characterized in that: The driving voltage power supply is a DC voltage source. A constant voltage is applied along the axial direction of the nanochannel through the Ag / AgCl electrode, driving the ions to move directionally along the axial direction of the nanochannel.

5. The isovalent ion screening system based on voltage-gated nanochannels according to claim 1, characterized in that: The first and second gated voltage sources are variable voltage sources that apply periodic voltages to the nanochannel walls through the metal electrode layer to control the surface potential of the nanochannel walls.

6. The isovalent ion screening system based on voltage-gated nanochannels according to claim 1, characterized in that, The specific steps for fabricating the nanochannel device are as follows: A1: A silicon nitride layer was deposited on a silicon substrate using dichlorosilane and ammonia via low-pressure chemical vapor deposition, and the thickness of the silicon nitride layer was observed by elliptic polarization spectroscopy. A2: A metal electrode layer was deposited on the silicon nitride layer by magnetron sputtering, and the thickness of the metal electrode layer was observed by a quartz crystal microbalance. A3: Then, a silicon nitride layer is deposited, followed by a metal electrode layer. This process is repeated to obtain a thin film in which the silicon nitride layer and the metal electrode layer are periodically stacked. The thickness of the silicon nitride layer and the metal electrode layer is controlled by changing the deposition time, temperature, and pressure. A4: By combining photolithography and reactive ion etching, a release window is created on the bottom silicon substrate using a potassium hydroxide solution; A5: By using focused ion beam technology to penetrate the thin film, a nanochannel is formed that runs through the silicon nitride layer and the metal electrode layer. The diameter of the nanochannel is adjusted by controlling the intensity and time of the ion beam. A6: Wires are led out from the edge of the metal electrode layer by electron beam induced deposition to facilitate connection to a gated voltage source; A7: Finally, connect the nanochannel device to the driving voltage power supply, gate voltage source one and gate voltage source two, and Ag / AgCl electrode, and place it between the electrolyte solution and the pure water solution to ensure that the solution in the two liquid pools can only flow through the nanochannel.

7. A method for isovalent ion screening based on a voltage-gated nanochannel isovalent ion screening system as described in claim 1, characterized in that, Includes the following steps: B1: A constant voltage is applied by a driving voltage power supply, so that isovalent ions are captured and enter the nanochannel and move along the nanochannel axis. The Ag / AgCl electrode on the electrolyte solution side is grounded. When screening isovalent cations, the voltage on the pure aqueous solution side is negative, and when screening isovalent anions, the voltage on the pure aqueous solution side is positive. B2: By adjusting the voltages of gated voltage source one and gated voltage source two, the surface potential of the nanochannel is adjusted, allowing ions to move through the nanochannel at different speeds with different ion diffusion coefficients. By applying a negative square wave pulse voltage to gated voltage source one and a positive square wave pulse voltage to gated voltage source two with the same pulse frequency, the ions are captured and released through multiple low-potential regions. The distance of the ions along the axial direction of the nanochannel gradually increases and they are completely separated, ultimately achieving ion screening.

8. The isovalent ion screening method according to claim 7, characterized in that, The specific process of step B2 is as follows: S1: When the first gate voltage source is negative and the second gate voltage source is positive, a Brownian ratchet-like surface potential is formed on the nanochannel wall. Isovalent ions are captured at the wall at the first low potential and stop moving. S2: When the voltages of gate voltage source one and gate voltage source two become 0, the ions are released by the wall and move slowly along the nanochannel axis under the constant voltage of the driving voltage power supply. The movement speed of the ions is proportional to the ion diffusion coefficient, that is, the ions with a larger diffusion coefficient move faster. S3: When the first gate voltage source is negative and the second gate voltage source is positive, a Brownian ratchet-like surface potential is formed on the nanochannel wall again. At this time, the slow-moving ions do not enter the second low potential region, while the fast-moving ions are close to the second low potential region. Therefore, the fast-moving ions are captured at the wall at the second low potential, while the slow-moving ions are still captured at the wall at the first low potential. The distance of different ions along the nanochannel axis changes. S4: The above process is repeated, and after being captured and released in multiple low potential regions, the distance between different ions along the axis of the nanochannel gradually increases and they are completely separated. Fast-moving ions move through the nanochannel, while slow-moving ions remain in the nanochannel or are captured in the first low potential region, thus achieving ion screening.

9. The isovalent ion screening method according to claim 7, characterized in that, For different degrees of diffusion coefficient difference, different silicon nitride layer thicknesses can be achieved by controlling the process during nanochannel fabrication. The positional differences caused by different ion diffusion coefficients can be further enhanced by adjusting the number of metal electrode layers. Alternatively, ion screening can be achieved by adjusting the square wave pulse size and frequency of gate voltage source one and gate voltage source two, as well as the voltage of the driving voltage power supply.

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